In technical applications such as, for example, a motor vehicle construction and the like, it is often necessary to quickly and reliably detect the location of a component which can be moved into two end positions relative to a stationary part using measurement engineering. For example, in passenger restraint systems of motor vehicles, it has to be checked whether a passenger is belted or not.
For this reason, the proper locking of the tongue of the safety belt, which tongue has been inserted into the belt lock, must be checked. Knowledge of the locking state of the belt lock is necessary to notify the passengers by a signal to put on and lock the safety belts. Since the introduction of safety airbags, information about the locking state of the safety belts has also been important for activation or deactivation of mechanisms for inflating driver and passenger airbags, as well as side and head airbags.
EP-B-1 585 276 discloses a belt lock whose locking state is monitored by a switch which can be mechanically actuated. The switch consists of a fixed contact sheet and a contact sheet which is made as a spring contact and which projects into the displacement path of a slide which can be moved into two end positions. The slide presses against a middle bent region of the spring contact in the case of locking, as a result of which one contact end which is hammer-shaped comes into contact with the fixed contact sheet. However, this known belt lock switch is susceptible to faults. If the spring contact is made too solid, it can disrupt the displacement motion of the slide and by blocking the slide in the middle position can even lead to a malfunction of the belt lock. Conversely, if the spring contact is made so thin that its inherent spring force cannot hinder the slide in any case, in operation of the motor vehicle it tends to rattle. There is also a certain risk that the middle bent region of the spring contact will deform over time. This can lead to the hammer-shaped contact end no longer coming into contact with the fixed contact sheet, and in this way the locking state of the safety belt will no longer be detected and/or displayed. In the worst case, the spring contact can even break due to continuous vibrations, which likewise leads to the locking state of the belt lock no longer being able to be detected.
DE 10 2010 039 960 A1 (corresponding to US 2011/0094067 A1) has proposed a belt lock for a safety belt system in which a switching arrangement which can be mechanically actuated is located in a lower shell of the belt lock housing which is formed from two housing shells. The switch arrangement has at least one fixed contact part and one switching contact part which can move relative to the fixed contact part and which in one end position of an ejector of the belt lock is acted upon by the fixed contact part. The movable switching contact part is made as a stable spring clip sheet with two axially running side webs and a transverse web and has at least two elbow-like bows which in one end position of the axially movable ejector are pressurized by the latter. In the bottom part of the frame of the belt lock, there are recesses of the elbow-like bows of the movable switching contact part. Due to the especially flat execution of the switching arrangement which can be mechanically actuated with only two interacting flat sheets, the space available in the lower shell is sufficient. Regardless of the fact that the two flat sheets are made very stable and can be mounted relatively easily in the lower shell, this arrangement for ascertaining the closing state of the belt lock is a purely mechanical design.
WO 2008/095320 describes a belt lock in which the closing state of the belt lock is monitored without contact using a solenoid-operated switch. The solenoid-operated switch is located underneath the frame of the belt lock in the region of a recess for the locking body for the belt lock tongue. According to one representation which is not detailed in the document, the solenoid-operated switch can be located on the bottom of the lower shell of the belt lock. The solenoid-operated switch has a magnet which is located in a housing and which is electrically conductive at least in areas and thus can conductively bridge two electrical contacts of two electrical conductors. By changing the location of the locking body, the magnet within the housing can be moved, as a result of which the electrical contact between the two conductors is interrupted or closed. The contactless monitoring of the locking state of the belt lock with a solenoid-operated switch is very efficient, but dictates a separate switching element, specifically a solenoid-operated switch, with a movable magnet which can be moved out of a first end position into a second end position when an attractor element is moved.
Mechanical switches and solenoid-operated switches, depending on their design, are more or less susceptible to vibrations and impacts as can occur especially in a motor vehicle. Mechanical switches, but also the solenoid-operated switch, have wear of the electrical contacts over time. This is a consequence of the mechanical abrasion and a certain erosion during opening and closing of the electrical contacts. Here, the rebound behavior of the mechanical switch and of the solenoid-operated switch also plays a part. Abrasion which occurs in the actuation of the switch can lead to contact difficulties. Fouling from the outside can also occur in mechanical switches.